1. Field of the Invention
The present invention relates to a stereoscopic display device and a display method.
2. Related Art
As a stereoscopic image or motion picture display device allowing display of a motion picture, so-called “a three-dimensional display”, ones of various systems have been known. In recent years, particularly, a demand for a display device of a flat panel type employing a system where dedicated eyeglasses or the like are not used is increasing. As a stereoscopic motion picture display device of such a type, there is known one using a principle of holography, which is difficult to be put in a practical use. A system where a beam controlling element is installed just in front of a display panel (a display device) whose pixel positions are fixed, such as a liquid crystal display device of a direct view type or a projection type or a plasma display device is known as a system which can be realized relatively easily. In this connection, the beam controlling element serves to control beams from the display panel to direct them to an observer.
The beam controlling element is generally called “a parallax barrier”, and it controls beams such that different images are seen according to an angle change even at one or the same position on the beam control element. Specifically, when only a left and right parallax (horizontal disparity) is applied, a slit or a lenticular sheet (a cylindrical lens array) is used, and when a vertical disparity is also included, a pinhole array or a lens array is used. The systems using the parallax barrier are also classified to a binocular system, a multiview system, an ultra-multiview system, an integral photography (hereinafter, also called “IP”) system. A basic principle common to these types is substantially the same as that used in a stereoscopic photograph invented about a hundred years ago.
In general, it is considered that a difference between the IP system and an LS (lenticular sheet) system is based upon whether pixels are present on an image plane or on a focal plane. In an actual design, particularly, in a case that there are many pixels, however, the difference between the image plane and the focal plane is in a range of 0.1 mm or less, even if there is no aberration, which not only makes it difficult to make a discrimination therebetween regarding precision but also makes it difficult to make a discrimination between presence and absence of beam converging at a viewing distance. The IP system described in this text means such a constitution that discrimination between positions of an image plane and a focal plane is not made but a position of a lateral viewpoint where a normal stereoscopic image can be seen at the viewing distance is arbitrary or continuous. Further, the multiview system described in this text is not equivalent to the LS system but it means such a constitution that a position of a lateral viewpoint where a normal stereoscopic image can be seen at the viewing distance is determined on the basis of an interpupilliary distance.
In both the IP system and the multiview system, since the viewing distance is usually finite, a display image is produced such that a perspective projection image at the viewing distance can be actually seen.
In the IP system, since a parallax barrier pitch Ps when viewed at a position of the eyes of an observer is not integer times a pixel-to-pixel pitch Pp, moire may be viewed when a black matrix is not ignored. In particular, when a slit or a lenticular sheet with a low aperture ratio of pixels in a horizontal direction is used, moire is easily seen. Even in the multiview system where the parallax barrier pitch Ps which can see at the viewing distance is integer times the pixel-to-pixel pitch Pp, when deviation occurs in a forward or rearward direction regarding the viewing distance, moire can see on a similar principle. However, it is known that, when the aperture ratio of pixels in a horizontal direction is 50% and the pixels have a delta arrangement, the moire can be cancelled and moire can be cancelled even in another pixel shape (for example, refer to Japanese Patent Laid-Open No. 7-15752). It is also known that moire is cancelled by inclining a lenticular sheet by an angle of about 9.5° (for example, refer to Japanese Patent Laid-Open No. 2001-501073). It is made possible to allocate parallaxes in a vertical direction, namely in two or more lines in a distributing manner by utilizing the delta arrangement or the lenticular sheet disposed obliquely, and such an advantage can also be obtained that the number of parallaxes is increased by reducing a difference in resolution between a vertical direction and a horizontal direction. Besides, it is known that moire or color moire can be reduced by using a diffusion film or defocusing (for example, refer to Japanese Patent Laid-Open No. 8-149520).
When a stereoscopic image is displayed, since original image data such as video images obtained by a plurality of cameras has a pixel arrangement constituted of a square arrangement like image data for an ordinary flat display and a shape of each pixel is square, it is desirable for conversion to a stereoscopic image conducted by fast image processing that effective pixels constitutes a square arrangement and each pixel itself is square even on a side of the stereoscopic display device. In the stereoscopic display device, in order to cause resolutions in a horizontal direction and in a vertical direction to match with each other, namely, in order to set an aspect ratio of effective pixels to 1, it is necessary to set the number of parallax to a multiple of 3, when a color filter has a stripe arrangement. However, when the number of parallaxes is set in this manner, there occurs a problem that color moire appears because a period of color of a color filter and a period of the parallax barrier along a horizontal direction are close to each other. As means for solving such a problem, there is proposed a method for shifting the number of parallaxes from the multiple of 3, but the aspect ratio of the effective pixel deviates from 1 in the method, which results in need for converting an image. As another solution, there has been proposed a method for applying a mosaic arrangement to a color filter.
Further, a system which allows switching of a stereoscopic display device between a stereoscopic display mode and a flat display mode has been disclosed. In such a disclosure, there have been known a method for performing switching of liquid crystal elements constituting a parallax barrier, a method for switching distances from a display plane of a lenticular sheet, a method of utilizing a liquid crystal lens, or the like.
As described above, in the conventional stereoscopic display devices, means for canceling moire have been disclosed in the above publications. However, it is a difficult problem that a aspect ratio of pixels is 1 and the pixels constitute a square arrangement for suppressing moire or color moire and attaining matching with a fast image processing, color data or information for each parallax is prevented from lacking, or a deviation in color distribution is canceled.
In the conventional stereoscopic display devices, there is still a problem that, when switching is performed between a flat image (two-dimensional) display and a stereoscopic image (three-dimensional) display, a resolution varies largely and an image quality at a time of flat display lowers due to deviation of a color distribution or the like.